man > tabs(1)

tabs(1)                                     User commands                                    tabs(1)

NAME
       tabs - set terminal tab stops

SYNOPSIS
       tabs [options] [tabstop-list]

DESCRIPTION
       The  tabs  program  clears  and  sets  tab-stops  on  the  terminal.   This uses the terminfo
       clear_all_tabs and set_tab capabilities.  If either is absent, tabs is  unable  to  clear/set
       tab-stops.  The terminal should be configured to use hard tabs, e.g.,

           stty tab0

       Like clear(1), tabs writes to the standard output.  You can redirect the standard output to a
       file (which prevents tabs from actually changing the tabstops), and later cat the file to the
       screen, setting tabstops at that point.

       These  are hardware tabs, which cannot be queried rapidly by applications running in the ter‐
       minal, if at all.  Curses and other full-screen applications may use hardware tabs  in  opti‐
       mizing their output to the terminal.  If the hardware tabstops differ from the information in
       the  terminal  database,  the  result  is unpredictable.  Before running curses programs, you
       should either reset tab-stops to the standard interval

           tabs -8

       or use the reset program, since the normal initialization sequences do not ensure  that  tab-
       stops are reset.

OPTIONS
   General Options
       -Tname
            Tell  tabs  which  terminal type to use.  If this option is not given, tabs will use the
            $TERM environment variable.  If that is not set, it will use the ansi+tabs entry.

       -d   The debugging option shows a ruler line, followed by two data  lines.   The  first  data
            line shows the expected tab-stops marked with asterisks.  The second data line shows the
            actual tab-stops, marked with asterisks.

       -n   This  option  tells  tabs  to check the options and run any debugging option, but not to
            modify the terminal settings.

       -V   reports the version of ncurses which was used in this program, and exits.

       The tabs program processes a single list of tab stops.  The last option to be processed which
       defines a list is the one that determines the list to be processed.

   Implicit Lists
       Use a single number as an option, e.g., “-5” to set tabs at the given interval (in this  case
       1, 6, 11, 16, 21, etc.).  Tabs are repeated up to the right margin of the screen.

       Use “-0” to clear all tabs.

       Use “-8” to set tabs to the standard interval.

   Explicit Lists
       An  explicit  list can be defined after the options (this does not use a “-”).  The values in
       the list must be in increasing numeric order, and greater than zero.  They are separated by a
       comma or a blank, for example,

           tabs 1,6,11,16,21
           tabs 1 6 11 16 21

       Use a “+” to treat a number as an increment relative to the previous value, e.g.,

           tabs 1,+5,+5,+5,+5

       which is equivalent to the 1,6,11,16,21 example.

   Predefined Tab Stops
       POSIX defines several predefined lists of tab stops.

       -a   Assembler, IBM S/370, first format
            1,10,16,36,72

       -a2  Assembler, IBM S/370, second format
            1,10,16,40,72

       -c   COBOL, normal format
            1,8,12,16,20,55

       -c2  COBOL compact format
            1,6,10,14,49

       -c3  COBOL compact format extended
            1,6,10,14,18,22,26,30,34,38,42,46,50,54,58,62,67

       -f   FORTRAN
            1,7,11,15,19,23

       -p   PL/I
            1,5,9,13,17,21,25,29,33,37,41,45,49,53,57,61

       -s   SNOBOL
            1,10,55

       -u   UNIVAC 1100 Assembler
            1,12,20,44

   Margins
       A few terminals provide the capability for changing their left/right margins.  The tabs  pro‐
       gram has an option to use this feature:

       +m margin
            The effect depends on whether the terminal has the margin capabilities:

            •   If the terminal provides the capability for setting the left margin, tabs uses this,
                and adjusts the available width for tab-stops.

            •   If  the terminal does not provide the margin capabilities, tabs imitates the effect,
                putting the tab stops at the appropriate place on each line.  The  terminal's  left-
                margin is not modified.

            If  the  margin parameter is omitted, the default is 10.  Use +m0 to reset the left mar‐
            gin, i.e., to the left edge of the terminal's display.  Before  setting  a  left-margin,
            tabs  resets the margin to reduce problems which might arise on moving the cursor before
            the current left-margin.

       When setting or resetting the left-margin, tabs may reset the right-margin.

FILES
       /usr/share/tabset
              tab stop initialization database

PORTABILITY
       IEEE Std 1003.1/The Open Group Base Specifications Issue 7 (POSIX.1-2008)  describes  a  tabs
       utility.  However

       •   This  standard  describes  a +m option, to set a terminal's left-margin.  Very few of the
           entries  in  the  terminal  database  provide  the  smgl   (set_left_margin)   or   smglp
           (set_left_margin_parm) capability needed to support the feature.

       •   There is no counterpart in X/Open Curses Issue 7 for this utility, unlike tput(1).

       The -d (debug) and -n (no-op) options are extensions not provided by other implementations.

HISTORY
       A tabs utility appeared in PWB/Unix 1.0 (1977).  A reduced version shipped in Seventh Edition
       Unix  (early  1979)  and in 3BSD (later the same year); it supported a “-n” option to set the
       first tab stop at the left margin.  That option is not documented by POSIX.

       The PWB/Unix tabs utility returned in System III (1980), and used built-in tables rather than
       the terminal database, to support a half-dozen hardcopy terminal (printer)  types.   It  also
       had  built-in  logic to support setting the left margin, as well as a feature for copying the
       tab settings from a file.

       Versions of the program in later releases of AT&T Unix, such as SVr4, added support  for  the
       terminal  database,  but retained the tables to support the printers.  In an earlier develop‐
       ment effort, the tab stop initialization provided by tset(1) (1982),  and  incorporated  into
       tput(1) uses the terminal database,

       The  +m  option  was documented in the POSIX Base Specifications Issue 5 (Unix98, 1997), then
       omitted in Issue 6 (Unix03, 2004) without express motivation, though an introductory  comment
       “and  optionally  adjusts  the  margin” remains, overlooked in the removal.  The tabs utility
       documented in Issues 6 and later has no mechanism for setting  margins.   The  +m  option  in
       ncurses  tabs differs from the SVr4 feature by using terminal capabilities rather than built-
       in tables.

       POSIX documents no limit on the number of tab stops.  Other implementations impose  one;  the
       limit  is  20  in  PWB/Unix's tabs utility.  While some terminals may not accept an arbitrary
       number of tab stops, ncurses tabs attempts to set tab stops up to the  right  margin  if  the
       list thereof is sufficiently long.

       The  “Rationale” section of the Issue 6 tabs reference page details how the committee consid‐
       ered redesigning the tabs and tput utilities, without settling on an improved  solution.   It
       claims that

            no  known  historical  version  of tabs supports the capability of setting arbitrary tab
            stops.

       Nevertheless, the feature described in subsection “Explicit Lists” above was  implemented  in
       PWB/Unix, and permits the setting of abitrary tab stops.

SEE ALSO
       infocmp(1), tset(1), ncurses(3NCURSES), terminfo(5)

ncurses 6.4                                  2023-12-23                                      tabs(1)